strength to push 400 watts

not much at all - 400w is nothing really. Holding 400w for 20 mins is another thing altogether though...

Here's the formula:

AEPF = 0.2248 * P*60 / (2*pi*C*CL)

where

AEPF is "average effective pedal force" measured in pounds,
P is power measured in watts,
C is cadence measured in rpm,
CL is crank length measured in meters.

So if we plug in P=400 watts, C=90rpm, CL=0.175 meters, we get AEPF=54.5 lbs. What this means is that both legs together have to average 54.5 lbs force over the whole pedal stroke. What will actually happen of course is that you will put out more force during each down stroke and less in the "dead zone" when crank is at top/bottom. Also during each down stroke one leg will be doing more work than the other. However, still you can see that this is not very much force for two legs so the answer is it doesn't take much strength. As mentioned above, the hard part of cycling is doing this over and over, 90rpm for a long time (like 20mins).

so there is little benefit in training force right?

You are correct - little benefit.

Quoted post said:

Originally Posted by swampy1970 [IMG]/img/forum/go_quote.gif[/IMG]

You are correct - little benefit.

Unless 54.5 lbs of pedal force is currently beyond him. That value does seem a little low, it'd be good if Ric Stern or one of the other power experts could chip in here.

Quoted post said:

Originally Posted by steve [IMG]/img/forum/go_quote.gif[/IMG]

Unless 54.5 lbs of pedal force is currently beyond him. That value does seem a little low, it'd be good if Ric Stern or one of the other power experts could chip in here.

If 54lb of force is beyond him then one hopes he lives in a bungalow...

The formula is correct; power = force x velocity, wth a conversion factor to get the result in lbs-force. For me, it's easier to use metric units, since a watt is defined as a newton-meter/sec.

Not so sure about the assumption that force is constant all the way around. Doesn't really matter though, because even if the peak force needed is 100 lbs, that's well within the strength capacity of normal adults. As swampy said, as long as you can walk upstairs, one leg after another, you've got enough strength.

The stair-climbing analogy is interesting. If I climb a set of stairs at a brisk rate of two stairs/second, that's a bit like a "cadence" of 60. If the riser on each step is 8 inches, that's 0.2 meters per step. So, at 2 steps/second, I'm climbing at 0.4 meters/sec. The force required is just my bodyweight, say 90 kg-force, or 882 newtons. 882 newtons x 0.4 m/sec = 353 watts. That kind of output is easy for me getting up to my second floor, but after just a few flights, it gets tough. Climbing 0.4 meters/sec is easy for a minute, but not easy to sustain for an hour.

the OP asked the question elsewhere and i answered with 56 lb, although i used 170 mm cranks in my answer.

anyway, if you can't generate 56ish lb you're either very small (less than 6 yr old small) or something is pretty wrong with you, such that cycling is the least of your concerns.

400w is a lot.

32Nm at 66rpm near the start of my ride today.

400w is a lot. I could not put out 400w at the end of my ride today. But I was reaching the top of the hill in a reasonable amount of time.

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Many people think that power as time goes to zero is a reasonable measure of ability. Unfortunately work done goes to zero also.